We have performed ultrastructural experiments to investigate the application of functionalized carbon nanotubes to deliver therapeutic drugs to oral cancer cells. The anti-cancer drug cisplatin was covalently bound to single walled carbon nanotubes (SWNTs) and these were in turn bound to epidermal growth factor (EGF), which is expressed at very high levels by oral cancer cells. Cultured head and neck squamous cell carcinoma (HNSCC) cells of epithelial origin incubated with the functionalized nanoparticles were prepared for electron microscopy by fixation in glutaraldehyde and osmium tetroxide, followed by dehydration and embedding in epon. Electron micrographs, recorded digitally using a 120 kV TEM, revealed that bundles of SWNTs had entered the cells. In most HNSCC cells the SWNT bundles were distributed throughout the cytoplasm, whereas some cells showed a higher concentration of nanotubes adjacent to the cell nucleus. The results confirmed lower resolution data obtained from confocal fluorescence microscopy but provided more detailed information about the subcellular structures associated with the nanotubes after entry. Scanning transmission electron microscopy (STEM) and x-ray nanoanalysis are also being performed to characterize individual nanotubes and to determine the distribution of bound platinum atoms. The ultrastructural data are being correlated with optical measurements and cell viability assays conducted in NIDCR.